Molecular oxygen reacts spontaneously in neutral solutions with certain metal-peptide complexes to oxidize the peptides. With copper(II) and nickel(II) complexes this O2 activation proceeds by copper(III) and nickel(III) species which catalyze the process. The mechanism, scope, and specificity of metal-peptide autoxidations will be studied for various oligopeptides along with the factors which determine the point of oxidation and the oxidation products. The copper(III) and nickel(III) complexes will be further characterized as solids and in solution to determine their stoichiometry, coordination geometry, electrode potentials and oxidation-reduction reactions. The photochemical properties of Cu(III)-peptides and the reasons for photochemical inhibition of the autoxidation of Cu(II)-peptides will be studied. The properties needed for long-term stability of Cu(III) and Ni(III) complexes will be examined. The overall objectives are to determine the mechanisms and biological significance of the spontaneous autoxidations as well as the normal and toxic roles of copper and nickel in their high oxidation states.